The present invention relates to the exhaust gas emitted from a turbomachine, and more particularly to a system and method of utilizing a turbomachine as a prime mover of the exhaust gas recirculated within an EGR system.
There is a growing concern over the long-term effects of Nitrogen Oxides (hereinafter NOx) and Carbon Dioxide (hereinafter “CO2”) and Sulfur Oxides (SOx) emissions on the environment. The allowable levels of emissions that may be emitted by a turbomachine, such as a gas turbine, are heavily regulated. Operators of turbomachines desire methods of reducing the levels of NOx, CO2 and SOx emitted.
Significant amounts of condensable vapors exist in the exhaust gas stream. These vapors usually contain a variety of constituents such as water, acids, aldehydes, hydrocarbons, sulfur oxides, and chlorine compounds. Left untreated, these constituents will accelerate corrosion and fouling of the internal components if allowed to enter the turbomachine.
Exhaust gas recirculation (EGR) generally involves recirculating a portion of the emitted exhaust stream through an inlet system of the turbomachine. The exhaust stream is then mixed with the incoming airstream prior to combustion. The EGR process facilitates the removal and sequestration of concentrated CO2, and may also reduce the NOx and SOx emission levels. Then the recirculated exhaust mixes with the incoming airstream to create an inlet fluid.
The exhaust stream that is recirculated during the EGR process generally exits the turbomachine at a temperature range of Up to about 1500 degrees Fahrenheit. These temperatures may be too high to allow the exhaust stream to be recirculated into the inlet section of the turbomachine. The EGR process reduces the temperature of the exhaust stream to an allowable range for recirculation into the turbomachine. The heat removed from the exhaust stream may be considered low value heat.
The temperature of the fuel consumed by a turbomachine is generally required to be within a specific range. The fuel may include, but is not limited to, various type of fuel oil, a natural gas, or a synthetic gas. The combustion systems of some turbomachine required a ‘heated’ fuel such as, heated natural gas. Generally, the natural gas supply does not heat the natural gas to the required temperature of the turbomachine. Here, a fuel heater(s) is used to increase the temperature of the natural gas to meet the turbomachine requirements. The fuel gas heater(s) require an energy source to operate. This energy source is typically a parasitic load and reduces the overall efficiency of the turbomachine site. An operator of the turbomachine site will appreciate if a source of low value heat is used to heat the natural gas, and/or other fuel consumed by the turbomachine.
For the foregoing reasons, there is a need for a system that reduces the parasitic load associated with heating the fuel consumed by a turbomachine integrated with an EGR system. The system should use low value heat to increase the temperature of the fuel consumed by the turbomachine.